Cathode material for Li-ion battery applications

ABSTRACT

A family of Li-ion battery cathode materials and methods of synthesizing the materials. The cathode material is a defective crystalline lithium transition metal phosphate of a specific chemical form. The material can be synthesized in air, eliminating the need for a furnace having an inert gas atmosphere. Excellent cycling behavior and charge/discharge rate capabilities are observed in batteries utilizing the cathode materials.

FIELD OF THE INVENTION

The present invention is concerned with a family of novel cathodematerials and a unique processing method for the materials synthesis forLi-ion batteries.

BACKGROUND OF THE INVENTION

Stoichiometric LiFePO₄ cathode material has been discussed for replacingLiCoO₂ type cathode material for lithium ion application because of thepotentially lower cost (Fe replacing Co) and the safer operatingcharacteristics of the material (no decomposition of the material duringcharging). However, present processing issues make the stoichiometricLiFePO₄ material expensive and difficult to produce. Presently, LiFePO₄materials suitable for lithium ion battery applications require thesynthesis utilizing high temperature heat treatment (>600° C.) under aninert atmosphere. Also, in order to increase the conductivity of thematerial, electrically conductive carbon is usually used for enhancingthe conductivity and therefore the electrochemical properties of thesynthesized material. The use of the inert atmosphere is a key factorthat assures the good quality of the materials because of its importancein relation to residual carbon in the material. None of the prior artteaches how to synthesize LiFePO₄ material in air, without a protectiveatmosphere, and how to provide good conductivity of the material andthus good electrochemical properties of a cathode formed of thematerial.

It is known to use olivine structured material to be the active materialfor a battery cathode, such as in U.S. Pat. No. 5,910,382. Also U.S.Pat. Nos. 6,723,470, 6,730,281, 6,815,122, 6,884,544, and 6,913,855, ingeneral, teach methods and precursors utilized for the formation ofstoichiometric LiFePO₄, or the substitution of cations for Fe. The abovepublications only show how stoichiometric olivine structured materialshaving different cation substitutions are synthesized. None of the priorart teaches how to synthesize phosphate materials having a defectivecrystalline structure, in air, which have consistent goodelectrochemical properties for use as an active material in a cathode ofa Li-ion battery.

In general, defects in the crystalline structure of a material canaffect the electrochemical property of the synthesized materialdrastically. A classical example is the synthesis of stoichiometricLiNiO₂. A deficiency of lithium would lead to Ni mispositioned on the Lisites therefore retarding the diffusivity of Li drastically and causingthe loss in capacity at certain rates. The influence of electrochemicalproperties caused by misposition of Ni on Li sites has been studied byChang et al. (Solid State Ionics, 112 (1998) 329-344), which is herebyincorporated herein by reference. Additionally, the concentration of thedefects can be affected by different processing precursors andprocessing protocols. For example, a solution processed precursor wouldin general possess higher reaction kinetics compared to conventionalsolid state processes and therefore exhibit lower defect concentration.The reason could be attributed to the fact that LiNiO₂ undergoes adecomposition reaction that causes loss of Li during heat treatment. Asa result, proper precursors that render high formation kinetics wouldthus decrease the defect concentration of the synthesized material(Chang et al., Journal of the Electrochemical Society, 149 (2002)A331-A338; 149 (2002) A1114-A1120), which is hereby incorporated hereinby reference. In the present example, although defects can physicallyretard the diffusivity of Li, the electronic structure of the materialcould also be affected by the presence of defects and thus theelectrical conductivity of the resultant material. It is thus shown thatfactors such as precursors, processing environment, processing protocolsand the kinetics of the reaction to the materials would affect defectconcentration and the properties of the resulting material. In thepresent invention, a family of defective lithium transition metalphosphate material that can be synthesized at low temperature in airatmosphere possessing excellent rate and cycling capability is created.The formation of defects is caused by incorporating various lithiatedtransition metal oxides with distinct stoichiometry.

OBJECTS OF THE INVENTION

It is an object of the present invention to produce a new family ofdefective lithium transition metal phosphate based cathode materialwithout the need for using a furnace having an inert gas atmosphere.

It is an object of the present invention to provide a method forproducing a defective lithium transition metal phosphate based cathodematerial without the need for using a furnace having an inert gasatmosphere.

It is a further object of the present invention to provide a method ofproduction which is easily scaled-up for commercial applications.

It is still a further object of the present invention to provide amethod of production to consistently produce a cathode material havingexcellent cycling behavior and charge/discharge rate capabilities in abattery fabricated from the cathode material.

SUMMARY OF THE INVENTION

The present invention is focused on the development of a family ofdefective lithium transition metal phosphate that can be easilysynthesized in air atmosphere at low temperature meanwhile possessingexcellent consistency, rate capability and cyclability. The methodincludes, a) providing a crystalline lithium transition metal oxide(layer structured or spinel structured), b) providing an intermediateas-synthesized material consisting starting chemicals of Li:Fe:P:C inmolar ratios of 1:1:1:2, c), combining and milling the above materialsso as to form a mixture of the materials in particulate form, and d)heating the material of step c) to form a cathode material of defectivelithium transition metal phosphate crystalline. The heating is carriedout in a vessel in air and surfaces of the material facing the air arecovered by a layer of inert blanket which is porous to air and escapinggases caused by the heating.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily apparent from the followingdescription of a preferred embodiment thereof shown, by way of exampleonly, in the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a furnace reaction vessel and aninert blanket for use in synthesizing the material of the invention;

FIG. 2 is an x-ray diffraction (XRD) pattern for conventional LiFePO₄cathode material of Example 1;

FIGS. 3( a) and 3(b) are graphs for showing the cycling behavior of atest battery fabricated from the cathode material of Example 1;

FIG. 4 is an XRD pattern for the LiNi_((0.92))Mg_((0.08))O₂ cathodematerial of Example 2;

FIG. 5 is an XRD pattern for the defective crystalline lithiumtransition metal phosphate cathode material of Example 3;

FIGS. 6( a) and 6(b) are graphs for showing the cycling behavior of atest battery fabricated from the cathode material of Example 3;

FIGS. 7( a) and 7(b) are XRD patterns for defective crystalline lithiumtransition metal phosphate having 10 wt % and 20 wt %, respectively, ofLiNi_((0.92))Mg_((0.08))O₂ as shown in Example 5;

FIGS. 8( a) and 8(b) are graphs for showing the cycling behavior of atest battery fabricated from the cathode material of Example 5 having 10wt % of Li Ni_((0.92))Mg_((0.08))O₂;

FIGS. 8( c) and 8(d) are graphs for showing the cycling behavior of atest battery fabricated from the cathode material of Example 5 having 20wt % of Li Ni_((0.92))Mg_((0.08))O₂;

FIGS. 9( a) and 9(b) are stacks of XRD patterns for comparing peakintensity for various cathode materials found in examples describedherein;

FIG. 10 is an XRD pattern for defective crystalline lithium transitionmetal phosphate created by dissolving 3 wt % of Li_((1+x))Mn_((2−x))O₄as described in Example 8;

FIGS. 11( a) and 11(b) are graphs for showing the cycling behavior of atest battery fabricated from the cathode material of Example 8.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the design of a furnace and a heat treatment environmentfor the synthesis of the materials presently disclosed. FIG. 1 showsreaction vessel 1, which is open to air in furnace 2. The furnace isopen to the atmosphere at 3 a and 3 b so as to maintain substantiallyatmospheric pressure in the furnace. Flow of gases into or out of thefurnace is dependent on heating and cooling cycles of the furnace andchemical reactions taking place with materials in the furnace. Air isfree to enter the furnace, and air and/or products of a chemicalreaction of materials 4 in the reaction vessel 1 are free to exit thefurnace. Materials 4 in vessel 1 react chemically during heating stepsto form cathode materials of the invention. Materials 4 in vessel 1,which face air found in the furnace, are covered by a layer of a hightemperature inert blanket 5, which is porous to air and escaping gasescaused by the heating step. Heating coils of the furnace are indicatedat 6.

In the present invention, Fe₂O₃, Li₂CO₃, and H₃PO₄ are particularlychosen as the starting materials for the synthesis of lithium transitionmetal phosphate. Reasons for the choice include a relatively low cost ofthe starting material and a chemical reaction that releases CO₂ and H₂O,that is: Fe₂O₃+Li₂CO₃+2H₃PO₄+½C→2 LiFePO₄+3/2CO₂+3H₂O. The released gasby-products during reaction can permeate through the porosity of thehigh temperature inert and porous blanket.

Stoichiometric LiFePO₄ is conventionally known as the “active material”in a cathode for use in a Li-ion battery. However, it has been foundthat the electrical conductivity of stoichiometric LiFePO₄ is not goodand the performance of the battery can be improved with the presence ofa material having good electrical conductivity along with the LiFePO₄Carbon is known to be a good material for improving the electricalconductivity of the cathode. It is known to provide an amount of C inthe starting material of the above-reaction, which is greater than thestoichiometric amount, so as to provide a residual amount of C with theproduced stoichiometric LiFePO₄ cathode material. However, for thereaction to take place at a rate which is reasonable for commercialproduction, a temperature of about 600° C. or more is required. At suchtemperature, decomposition of carbon (for example carbon black) can takeplace, and the amount of residual C cannot be well controlled. It isknown to carry out the synthesis in a controlled inert atmosphere,however commercially producing the material in such a manner addssubstantial cost to the production. In the present invention a methodhas been found to produce a family of novel cathode materials withoutthe use of the above-described controlled atmosphere equipment andprocess.

In the present invention, a method is provided for making defectivelithium transition metal phosphates having a defective crystallinestructure that does not require high temperature heat treatment as wellas inert atmosphere condition. The way to create the defective structureis to dissolve other lithiated materials with different stoichiometryinto a LiFePO₄ structure. The chemistry is proposed as follows:xLiNiO₂+(1−x)LiFePO₄→LiNi_(x)Fe_((1−x))P_((1−x))O_(2(2−x))In this case, P and O are deficient and some vacancies would form asindicated by the subscripts shown for P and O. Or,x/2LiMn₂O₄+(1−x)LiFePO₄→Li_((1−x/2))Mn_(x)Fe_((1−x))P_((1−x))O_(2(2−x)).

In this case, Li and P and O are deficient and some vacancies would formin the similar way as mentioned in the previous reaction. The reactionsproposed are just utilized in explaining the occurrence of defectivestructured material. However, in the present invention, the target isnot to synthesize stoichiometric LiFePO₄. As a result, the layerstructured or spinel structured lithium transition metal oxides arereacting with an intermediate as-synthesized material that has a molarratio of Li:Fe:P:C=1:1:1:2.

In order to facilitate the formation of the above-mentioned defectivematerials in normal air environment, low temperature heat treatment isutilized for the synthesis. The meaning of low temperature implies justenough temperature for the formation of desirable material. In thepresent invention, the temperature is chosen to be between 550 to 650°C., preferably at 600° C. Too high of a temperature not only increasesenergy consumption, but also increases the difficulties in maintainingthe consistency of the synthesized material.

Features of the present invention include:

-   -   A. No use of an inert atmosphere: This feature results in:        -   i. Easy scale up for production.        -   ii. Much lower cost of a furnace since a gas-tight furnace            becomes unnecessary. Also, the cost of inert gas can be            saved.        -   iii. Overall cost of the synthesis protocol is reduced.        -   iv. Easy control of the quality of the resultant materials.    -   B. Good performance of the synthesized material: Excellent        cycling behavior (cycle life) and rate capability (>20C of rate        capability) are achieved as will be described in detail in the        examples below.    -   C. Consistency in performance: This is extremely important for        the synthesis of the material since the consistency of the        performance is extremely important for battery applications.        Owing to the formation of the defective crystalline structured        material, not only the conductivity of the as-synthesized        material is enhanced, but also the batch to batch consistency of        the as-synthesized materials is obtained, especially when heat        treated in an air environment.

The choice of a low temperature heat treatment can minimize thepossibility of decomposition of the desirable defective material.Besides, lower temperature heat treatment (lower than the decompositiontemperature of carbon black at ˜600° C.) can also reduce the variationsof residual carbon content and distribution during the heat treatment.It should be noted that although variations in the carbon content of thefinal product in the present invention is not as important as in priorart materials, owing to the high electrical conductivity of thedefective material, low temperature heat treatment is still recommendedfor minimizing unnecessary variations.

In the present invention the purpose of adding layer structured orspinel structured materials during synthesis is to create a defectivecrystalline structure of the resultant material. The importance of thecreation of defective crystalline structure is to promote the occurrenceof the change of band structure and thus the electrical conductivity ofthe resultant material. An earlier publication by the present inventorusing a computational method, pointed out that the electrochemicalproperty of the material could be influenced significantly by the anions(Chang et al., Journal of the Electrochemical Society, 151 (2004)J91-J94), which is hereby incorporated herein by reference. Because ofthe above-described enhancement of electrical conductivity of thedefective material, the use of excess carbon and the existence of carboncontent in the resultant material become unimportant or unnecessary.

In the present invention a new family of defective crystalline structurelithium metal phosphate materials, that can be obtained using an airenvironment heat treatment, is provided. Excellent electrochemicalproperties are exhibited. The high rate capability has been demonstratedto be more than 20C.

Following are examples of cathode materials, both prior art materialsand cathode materials of the invention.

EXAMPLE 1 Synthesis of Conventional Stoichiometric LiFePO₄ using ExcessCarbon under Inert Atmosphere

Fe₂O₃ and Li₂CO₃ and Super P (carbon black), molar ratio of (1:1:2) weremixed together with the addition of a suitable amount of water toproduce a slurry. After mixing thoroughly, the proper Stoichiometricamount of phosphoric acid was added in the solution and extended mixingwas utilized. Finally, the slurry was dried in air at 150° C. for 10hours followed by further heat treatment at 400° C. for 5 hours untilchunks of materials were obtained. The as-prepared material was thensubjected to grinding and ball milling for about 12 hours.

Heat treatment for synthesis was conducted in a sealed metallic box withthe flow of nitrogen gas. The materials were heat treated at 650° C. for10 hours under the nitrogen gas flow.

XRD data is shown in FIG. 2. It is observed that phase pure material canbe obtained using the described conventional heat treatment protocol.Battery data (obtained using a three electrode design test battery andlithium as the reference electrode) is shown in FIG. 3. From FIG. 3( a)it can be seen that the capacity is high during the firstcharge-discharge cycle (˜C/5 rate, 0.23 mA/cm²). The cycles followingthe first cycle were tested using ˜2C test conditions (2.3 mA/cm² inconstant current charge and discharge, with constant voltage charge tocurrent <200 uA during the charge step). From FIG. 3( b) it can beobserved that the cycle life was not good. The capacity fades from (˜80mAh/g to ˜65 mAh/g after 15 cycles). The fade in capacity is anindication of insufficient electrical conductivity of the material thatcan not sustain high current cycling and thus fade in capacity resultsduring cycling. This result is consistent with the prior art disclosedin U.S. Pat. No. 6,723,470.

EXAMPLE 2 Synthesis of LiNi_(0.92)Mg_(0.08)O₂

Stoichiometric amounts of LiOH, H₂O, Ni(OH)₂ and Mg(OH)₂ were mixed in ablender. After 3 hours of mixing, the as-mixed precursor materials weresubjected to heat treatment in air at 600° C. for 10 hours. After gentlecrushing and sieving, the materials were then heat treated again inoxygen at 700° C. for 24 hours.

An XRD pattern of the as-synthesized materials is shown in FIG. 4. FromFIG. 4 it can be seen that the as-synthesized material is phase pure innature. This suggests that all Mg cations are dissolved in the LiNiO₂structure. According to the inventor's earlier publication referred toabove, the Mg cations are substituting at the transition metal sites.

EXAMPLE 3 Synthesis of Defective Lithium Transition Metal PhosphateObtained by Incorporating 3 wt % of LiNi_(0.92)Mg_(0.08)O₂ and HeatTreating in an Air Environment

Fe₂O₃, Li₂CO₃ and Super P (carbon black), molar ratio of (1:1:2) weremixed together with the addition of a suitable amount of water toproduce a slurry. After mixing thoroughly, a stoichiometric amount ofphosphoric acid was added to the mixture and extended mixing wasutilized. Finally, the slurry was dried in air at 150° C. for 10 hoursfollowed by further heat treatment at 400° C. for 5 hours until chunksof material were obtained. The as-synthesized intermediate material wasthen subjected to grinding and ball milling with 3 wt % ofLiNi_(0.92)Mg_(0.08)O₂ prepared as described in EXAMPLE 2, for about 12hours.

Synthesis of the material was carried out by heat treatment at 600° C.for 10 hours in the furnace shown in FIG. 1, under air atmosphere.

XRD data is shown in FIG. 5. The phase pure nature of the materialsynthesized is verified by comparing the present XRD data with the XRDdata shown in FIG. 2. It is clear that a full dissolution of the layerstructured LiNi_(0.92)Mg_(0.08)O₂ into the LiFePO₄ is possible. A fulldissolution explains the formation of phosphorous and oxygen vacanciesduring processing. The electrochemical data is shown in FIGS. 6( a) and6(b). From FIG. 6( a) it can be seen that the cycling behavior is muchimproved compared to the data shown for EXAMPLE 1 in FIGS. 3( a) and3(b). No fade in capacity was observed (see FIG. 6( b)), as overlappingof cycling curves is observed. This result suggests that good electricalconductivity of the material is maintained throughout the cycling andthus the material has no fade characteristics. Aside from theimprovement in cycling behavior, it is observed that the averagedischarge voltage has been increased from 3.28V to 3.33V at a 2 Cdischarge rate. This increase suggests that the defective crystallinematerial has distinct structure and property characteristics incomparison to the conventional stoichiometric LiFePO₄. Furthersupportive evidence is presented in EXAMPLES 6 and 7.

EXAMPLE 4 Fabrication of a 1.5 Ah Battery using the Material of theInvention Synthesized in Example 3

Cathode preparation: 5 wt % of Super P (500 g) and 5 wt % (500 g) ofPVDF were mixed thoroughly with 90 wt % (9 kg) of the material of theinvention using NMP as a solvent. After stirring and mixing for about 12hours, a homogeneous slurry was obtained. The slurry had a viscosity of˜20,000 cp prior to coating. The slurry was coated on an aluminum foilusing a comma coater. The coated film was dried at 140° C. forapproximately 10 minutes in a convective furnace. Similarly, the otherside of the aluminum foil was coated with the same material. Afterdrying, the coated foil was subjected to rolling. The resultingcompressed films and foil had a thickness of 160±5 um.

Anode preparation: 8 wt % of PVDF and 92 wt % of natural graphitematerial were mixed thoroughly using NMP as a solvent. After stirringand mixing for about 12 hours a homogeneous slurry was obtained. Theslurry had a viscosity of ˜15,000 cp prior to coating. The slurry wascoated on a copper foil using a comma coater. The coated film was driedat 140° C. for approximately 10 minutes in a convective furnace.Similarly, the other side of the copper foil was coated with the samematerial. After drying, the coated foil was subjected to coating with apolymer solution as disclosed in the Applicant's earlier U.S. Pat. No.6,727,017. The as-coated anode was subjected to rolling to a thicknessof 210±5 um.

Battery assembly: A battery was made using 28 pairs of cathodes (4 cm×5cm) and anodes (4 cm×5 cm). The electrodes were placed in an alternatingsequence, as in ABABAB fashion. After soaking with an electrolyte(EC/DMC 1:1) for about 12 hours, the battery was subjected to cycling.

Table 1 shows the cycling behavior of the resultant battery. The batteryshows a capacity of ˜1200 mAh at a charge/discharge current of 1.5 A.The average voltage of the battery during charge/discharge is also shownin Table 1.

TABLE 1 CYCLING BEHAVIOR OF THE BATTERY OF EXAMPLE 5 Cycling BehaviorDuring Formation Without Aging (4 cycles only) Dis- Average AverageCycle Charge Discharge Charge charge Charge Discharge Num- CapacityCapacity Energy Energy Voltage Voltage ber (Ah) (Ah) (Wh) (Wh) (V) (V) 11.2719 1.1872 4.5453 3.6899 3.57E+00 3.11E+00 2 1.1730 1.1676 4.15883.6294 3.55E+00 3.11E+00 3 1.1535 1.1549 4.0825 3.5912 3.54E+00 3.11E+004 1.1391 1.1505 4.0269 3.5791 3.54E+00 3.11E+00

The battery was subjected to a high rate capability test at >20 C asfollows:

Test setup and configuration: 7 light bulbs (12V, 50 W for each bulb)were connected in series one voltage meter and one ampere meter formonitoring the voltage and current. Four of the batteries of Example 4were also connected in series and a total voltage of 13.2V was obtained(prior to closing the circuit). On closing the circuit an initial amperemeter reading of <30 Amp and a voltage reading of 10.5V (a total of 315W) was observed. After 10 seconds, the readings of the ampere meterdropped to 28 A and the voltage reading dropped to 10.2V (a total of 286W). Thereafter, the readings remained stable for the next 20 seconds.

From the high rate discharge test results described above, it can beconcluded that the batteries possessed a high rate capability with adischarge capability of >20 C (a 1 C rate is 1.5 A, 20 C rate is 30 A).This result is significant in revealing that a good cathode material isobtainable under air atmosphere, that possesses high rate capabilities.Potential uses of such batters are power tools, vehicles, andlarge-scale family use power batteries.

EXAMPLE 5 Additional Example showing the Synthesis of Defective LithiumTransition Metal Phosphate Obtained by Incorporating 10 wt % and 20 wt %of LiNi_(0.92)Mg_(0.08)O₂ and Heat Treating in an Air Environment

The same processing protocols found in EXAMPLE 3 were utilized for thesynthesis of defective lithium transition metal phosphate with additivesof 10 wt % and 20 wt %, in place of 3 wt % of Example 3.

XRD data is shown in FIGS. 7( a) and 7(b). Stronger impurity phasepatterns are observed for the 10 wt % and 20 wt % LiNi_(0.92)Mg_(0.08)O₂added samples compared to the XRD data shown for pure LiFePO₄ and 3 wt %LiNi_(0.92)Mg_(0.08)O₂ incorporated material (FIGS. 2 and 5,respectively). This suggests that the existence ofLiNi_(0.92)Mg_(0.08)O₂ during synthesis could result in some impurityphases including un-reacted LiNi_(0.92)Mg_(0.08)O₂ and partiallydissolved material.

Electrochemical data is shown in FIGS. 8( a)-8(d). From FIG. 8 it can beseen that the cycling behavior is as good as the 3 wt %LiNi_(0.92)Mg_(0.08)O₂ incorporated material, although the capacitydecreased from 75 mAh/g to 50˜60 mAh/g range. It can be concluded thatwith the addition of more LiNi_(0.92)Mg_(0.08)O₂ material, although goodelectrical conductivity of the material is ensured, owing to thepresence of the defective crystalline structure, with too muchLiNi_(0.92)Mg_(0.08)O₂, addition or insufficient heat treatment timewould lead to the existence of un-reacted LiNi_(0.92)Mg_(0.08)O₂ notpossessing any capacity. As a result, for the purpose of good control ofthe performance of the defective lithium iron phosphate type materialsynthesized in an air environment, the proper amount ofLiNi_(0.92)Mg_(0.08)O₂ should be added for achieving the best electricalconductivity and capacity of the material. The amount ofLiNi_(0.92)Mg_(0.08)O₂ addition during synthesis is thus very importantfor obtaining the best electrochemical performance in a battery.

EXAMPLE 6 Comparative Study of Defective Lithium Transition MetalPhosphate (Resulting from Reactions with Different Amounts ofLiNi_(0.92)Mg_(0.08)O₂), and LiFePO₄ Simply Mechanically Mixed withLiNi_(0.92)Mg_(0.08)O₂ to Different Weight Percentages

FIG. 9( a) shows a stack of XRD patterns of the conventionallysynthesized LiFePO₄ (prepared as shown in EXAMPLE 1), defective lithiumtransition metal phosphate having 3 wt % LiNi_(0.92)Mg_(0.08)O₂(prepared as shown in EXAMPLE 3), defective lithium transition metalphosphate having 10 wt % and 20 wt % LiNi_(0.92)Mg_(0.08)O₂ (prepared asshown in EXAMPLE 5).

FIG. 9 b shows a stack of XRD patterns of 0 wt %, 3 wt %, 10 wt %, and20 wt % LiNi_(0.92)Mg_(0.08)O₂ simply mechanically added and mixed withconventional stoichiometric LiFePO₄. From FIG. 9( b) it can be seen thatwith a slight LiNi_(0.92)Mg_(0.08)O₂ addition (3 wt %), distinctLiNi_(0.92)Mg_(0.08)O₂ peaks can be observed (˜18.6° for (003) and 44.4°for (104)). This result suggests that the phase pure nature of the 3 wt% LiNi_(0.92)Mg_(0.08)O₂ reacted sample (Example 3) is the result oftotal dissolution of LiNi_(0.92)Mg_(0.08)O₂ into the LiFePO₄ structure,therefore rendering the presence of phosphorous and oxygen vacancies asdiscussed. Also, with the same amount of LiNi_(0.92)Mg_(0.08)O₂ additionin either case, (material of FIG. 9( a) and material of FIG. 9( b)), theLiNi_(0.92)Mg_(0.08)O₂ added (un-reacted) sample always shows higher(003) and (104) peak intensity (˜18.6° and 44.4°). This suggests thatdefective lithium transition metal phosphate is a consequence ofreactions between the as-synthesized precursor materials (as describedin EXAMPLE 3 and 5). The characteristics are distinct from materialsimply mechanically mixed with LiNi_(0.92)Mg_(0.08)O₂ to differentweight percentages.

EXAMPLE 7 Chemical Analyses for Conventional LiFePO₄ (Material Made inEXAMPLE 1) and Defective Lithium Transition Metal Phosphate Synthesizedby Incorporating 3 wt % LiNi_(0.92)Mg_(0.08)O₂ (Material made in EXAMPLE3)

The chemical analysis results for both conventional LiFePO₄ (materialmade in EXAMPLE 1) and defective lithium transition metal phosphateincorporated with 3 wt % LiNi_(0.92)Mg_(0.08)O₂ (material made inEXAMPLE 3) are shown in Table 2. The calculated stoichiometry numbersfor the two samples are obtained by converting the wt % to mol % foreach element while setting the stoichiometry of Fe and (Fe+Ni+Mg) tounity. In the case of conventional LiFePO₄, the calculated stoichiometryratio of Fe:P=1:0.9805. Similarly, the 3 wt % incorporated materialpossesses a stoichiometry ratio of Li:(Fe+Ni+Mg):P=1:0.9534. Adeficiency of phosphorous supports the proposed formation of vacanciesduring the reaction. It should be noticed that the oxygen content cannot be analyzed chemically. However, if we assume a 100 wt % of thesample being analyzed, the stoichiometric numbers for the 3 wt %incorporated material is still smaller than the conventional material.This is still consistent with the proposed oxygen vacancy formationduring the synthesis.

TABLE 2 Chemical analyses for materials synthesized in EXAMPLE 1 andEXAMPLE 3*^(†) Example 1 Mol Example 3 Mol Elements material fractionElements material fraction Li (wt %) 4.3 0.61951 Li (wt %) 4.14 0.59646Fe (wt %) 32 0.57299 Fe (wt %) 31.0 0.55509 P (wt %) 17.4 0.56183 P (wt%) 17.3 0.55861 C (wt %) 5.7 0.47460 C (wt %) 4.45 0.37052 Ni (wt %)1.67 0.028455 Mg (wt %) 0.57 0.00234 Molar 1:0.9805 Molar 1:0.9534 ratioratio of of Fe:P (Fe + Mg + Ni):P *The Li, Fe, P, Ni, and Mg wereanalyzed using ICP-OES The C was analyzed using ASTM D5373 ^(†)Theoxygen content can not be determined directly owing to the relativelyhigh concentrations of metals.

EXAMPLE 8 Synthesis of Defective Lithium Transition Metal PhosphateIncorporated with Spinel Structured Li_(1.07)Mn_(1.93)O₄ (3 wt %) in AirEnvironment

Fe₂O₃, Li₂CO₃ and Super P (carbon black), molar ratio of (1:1:2) weremixed together with the addition of a suitable amount of water. Aftermixing thoroughly, a stoichiometric amount of phosphoric acid was addedto the solution and extended mixing was utilized. Finally, the slurrywas dried in air at 150° C. for 10 hours followed by further heattreatment at 400° C. for 5 hours until chunks of materials wereobtained.

Li_(1.07)Mn_(1.93)O₄ was synthesized using Li₂CO₃, and Mn₃O₄ with astoichiometric ratio of Li:Mn of 1.1:2 in the precursor. The startingmaterials Li₂CO₃ and Mn₃O₄ were first mixed using a ball mill for 8hours, followed by heat treating the material to 800° C. for 24 hours inair. The material obtained was then subjected to grinding and sieving.

The materials prepared above were then subjected to grinding and ballmilling for about 12 hours with the amount of Li_(1.07)Mn_(1.93)O₄ being3 wt %. Further heat treatment at 600° C. for 10 hours in the furnaceshown in FIG. 1 under air atmosphere was conducted on the materials.

The XRD data is shown in FIG. 10. Slightly more impurity phases areobserved compared to the XRD data shown for pure LiFePO₄ and 3 wt %LiNi_(0.92)Mg_(0.08)O₂ incorporated material. Electrochemical data isshown in FIGS. 11( a) and 11(b). From FIG. 11( a) it can be seen thatthe cycling behavior is much improved compared to the data shown inEXAMPLE 1. No fade in capacity was observed (see FIG. 11( b)), asoverlapping of cycling curves is observed. This result suggests thatgood electrical conductivity of the material is maintained throughoutthe cycling and thus the material possesses no fade characteristics.

While specific materials, heat treatments, etc. have been set forth forpurposes of describing embodiments of the invention, variousmodifications can be resorted to, in light of the above teachings,without departing from the Applicant's novel contributions; therefore indetermining the scope of the present invention, reference shall be madeto the appended claims.

1. A method for forming a cathode material for a lithium-ion battery,comprising the steps of a) providing a crystalline lithium transitionmetal oxide, b) providing starting chemicals of Li:Fe:P:C in a molarratio of 1:1:1:2, c) combining and milling the materials of a) and b) soas to form a mixture of the materials of a) and b) in particulate form,d) heating the material of step c) to form a cathode material having adefective crystalline structure of crystalline LiFe_((1−x))M_(x)P_((1−x))O_(2(2−x)) orLi_((1−x/2))M_(x)Fe_((1−x))P_((1−x))O_(2(2−x)), wherein 0.01 ≦x ≦0.3, Mis one or more elements selected from the group of metals consisting ofnickel, titanium, vanadium, chromium, manganese, iron, cobalt andaluminum, and said heating is carried out in a vessel in air; andsurfaces of the material facing the air are covered by a layer of inertblanket which is porous that allows air permeation and escaping gasescaused by said heating.
 2. The method of claim 1, wherein the startingchemicals of step b) include Fe₂O₃, Li₂ CO₃, H₃ PO₄, and C, Fe₂ O₃ +Li₂CO₃ and H₃ PO₄ are provided in stoichiometric amounts, and C is providedin an amount exceeding a stoichiometric amount.
 3. The method of claim1, wherein in step d) the materials are heated to a temperature ofbetween 550° C. and 650° C. for a period of between 8 and 12 hours. 4.The method of claim 1, wherein step b) further includes, forming andmixing a slurry of the starting chemicals, drying the slurry, heatingthe dried slurry to obtain a product suitable for milling in step c). 5.The method of claim 4, wherein the slurry is dried in air at about 150°C. for about 10 hours, and the dried slurry is heated at about 400° C.for about 5 hours.
 6. The method of claim 1, wherein said crystallinelithium transition metal oxide has a general chemical formula of LiNi_((x))Mg_((1−x))O₂ or Li_((1+x)) Mn_((2−x))O₄, wherein 0 ≦x≦0.2. 7.The method of claim 6, wherein said crystalline lithium transition metaloxide is Li Ni_((0.92))Mg_((0.08))O₂ or Li_((1.07))Mn_((1.93))O₄.
 8. Themethod of claim 1, wherein said blanket is a ceramic fiber blankethaving a layer thickness of about 1-3 inches.
 9. The method of claim 1,wherein in step d) the materials are heated to a temperature of about600° C. for a period of about 10 hours.
 10. The method of claim 1,wherein the mixture of step c) contains 1-5 wt % of the crystallinelithium transition metal oxide.